Using such a method, which is known from U.S. Pat. No. 6,752,946 B2, such a device is made by means of insert injection moulding. First, the flexible foil is inserted into a mould. During the moulding process, a polymer is heated up, liquefied and injected into the mould against one side of the foil. After injecting the polymer and providing it with the desired shape, the polymer is cooled down and solidified to form the housing wall. When the polymer changes from a hot liquid into a cool solid housing wall, the total volume of the polymer will be reduced; the percentage of the reduction of the total volume of the polymer is presented as the shrinkage factor. The polymer will adhere to the foil during injection moulding. After the injection moulding process, at the area where the polymer is present, the foil will shrink together with the polymer. At the location of the hole, where no polymer is present, the flexible part of the foil extending over the hole is not heated as much as the polymer and will almost not shrink after the injection moulding process. As a result of the combination of the foil and a polymer housing wall which has been shrunk and the flexible part of the foil extending over the hole, which flexible part almost has not shrunk, the flexible part will be formed into a dome-shaped bump.
A disadvantage of the known device is that such a dome-shaped bump results in an uneven surface of the foil. Furthermore, additional measures need to be taken in order to be able to use the dome-shaped bump as a displaceable operating member and to ensure good pressing feeling.